This invention relates to thermoplastic polymer materials for the preparation of three-dimensional prototypes or models. Prototypes of parts are made and used in testing in a wide-variety of industries, such as the automobile, aerospace, and biomedical prostheses manufacturing industries. After successful testing the prototypes of parts, a mold of the prototype can be made and the part can be manufactured on a mass production basis.
There are three ways of making prototypes. One method involves simply making a mold of the part, making the prototype, and then testing the prototype. However, this method requires the cost of making a mold, which itself can be extremely expensive and time-consuming. Moreover, this method may require numerous molds to be made on a trial and error basis until a successful part has been designed that sufficiently passes the required testing.
A second method of making prototypes involves sculpting a three-dimensional prototype of a particular shape from a block work piece. In this method, the prototype is drawn either manually or using computer-aided design (CAD) techniques, and the prototype is formed by removing material from a block work piece. The part can be further machined either manually or using computer-aided machining (CAM) techniques. However, this method can also be a costly and time-consuming process because it may require repeated iterations until a desired prototype is made.
A third method that has been developed involves the formation of a three-dimensional prototype by depositing multiple layers of a material in a fluid state onto a base. The fluid solidifies to define the prototype element. In general this method is often termed freeforming in the prior art. For example, such a method is taught in U.S. Pat. No. 5,340,433, and U.S. Pat. No. 5,121,329, both issued to S. Scott Crump and assigned to Stratasys, Inc. incorporated herewith by reference. In this method, a layer of the fluid material solidifies and then another layer of fluid material is deposited over the preceding layer. The thickness of each layer is controlled by the distance between the tip of the dispensing head and the preceding layer. However, there are a number of disadvantages to the method and apparatus taught in this third method because only certain types of materials can be suitably used to make the prototypes, such as waxes having low melt viscosity and strength. Thermoset materials may be used to try to improve strength and toughness. In any event, this prior art deposition method may not produce durable prototypes made from high performance engineering polymers and composites.
There is a clear need for a method and apparatus that can make stronger and tougher prototypes made of engineering polymers and composites having high melt viscosity and long chain lengths. Such a method and apparatus is disclosed in U.S. Pat. No. 6,067,480, which is incorporated herein by reference.
As noted in U.S. Pat. No. 6,067,480, materials for high pressure fused deposition include polyaryletherketone (PEEK(copyright) produced by Victrex), polmethylmethacrylate (PMMA(copyright) produced by DuPont), polycarbonate (Lexan(copyright) made by General Electric Plastics), thermoplastic polyurethane (Pellethane(copyright) made by Dow Chemical), and polylatic acid/polyglycolic acid block copolymer (a bio-absorbable material made by a Biomet joint venture). Fused deposition of fiber reinforced grades of engineering polymers and composites, for example PEEK(copyright) and Lexan(copyright) can also be used for the invention disclosed in U.S. Ser. No. 08/825,893. Moreover, prototypes can be made in accordance with that invention using fiber reinforcement. For example, carbon fiber reinforced PEEK(copyright) materials had a tensile strength of over 36,000 psi, exhibited a very high fracture toughness and demonstrated highly anisotropic mechanical properties whereas unreinforced materials did not.
Thus, there is a clear need for strong materials that can be used in a method for making prototypes, and in particular materials for the method involving the depositing of multiple layers in a fluid state onto a base. More specifically, there is a need for strong thermoplastic polymers that can be easily melt extruded by an extrusion freeforming apparatus in layer form, and which then solidify upon cooling so that complicated shaped parts can be freeform fabricated by precisely and sequentially depositing polymer layers upon one another until the desired component is produced. There is also a need for strong materials that can be used as a support material for use in an extrusion freeforming apparatus that prevents the sagging of deposited molten, prototype material layers before cooling and solidification. Support materials are particularly important when fabricating complex geometry, dimensionally accurate prototypes having numerous overhangs, or internal cavity features.
In the present invention, a unique thermoplastic polymer material, i.e., poly(2-ethyl-2-oxazoline) (referred to hereafter as xe2x80x9cPEOxe2x80x9d), is used as a polymer layer material as well as a support material in a freeform fabrication process. More specifically, PEO is melt extruded by a freeforming apparatus in layer form. The PEO layers solidify upon cooling and complicated shaped parts can be freeform fabricated by precisely and sequentially depositing polymer layers upon one another until the desired component is produced. Thus, prototypes can be directly free formed by an extrusion freeforming apparatus using PEO as a raw material.
In addition, in the present invention, PEO is used as a support material for use in rapid prototype processes such as extrusion freeform fabrication or a a fused deposition modeling process. In particular, many parts which are fabricated by these processes have complicated overhang geometries which require the use of a support material that prevents the sagging of deposited molten, prototype material layers before cooling and solidification.
It has been discovered that a major advantage of PEO over other materials is that PEO is a high strength rigid thermoplastic polymer that is easily and accurately extruded and has a good slump resistance at temperatures less than about 200xc2x0 C. PEO also has the added benefits in that it is essentially an amorphous polymer that does not undergo significant shrinkage upon solidification. Polyethylene oxide, another commercially available water soluble thermoplastic, on the other hand, undergoes approximately 15-20% shrinkage due to crystallization upon solidification. Shrinkage on the order of this magnitude puts a great deal of stress and may induce warpage in free formed support material layers. PEO also has high degree of interlayer adhesion when free formed. Polyethylene oxide has negligible interlayer adhesion when free formed. A major benefit of using PEO is that it has all of the above properties coupled with high water solubility. Rapid prototype parts can therefore be fabricated using PEO as a support material and the PEO support can be easily washed away with water from the completed prototype part without employing toxic and environmentally detrimental solvents, which may also dissolve the desired polymer prototype part. It is believed that PEO is the only commercially available non-ionic water soluble thermoplastic material (sold under the tradename Aquazol by Polymer Chemistry Innovations Inc., of Tucson, Ariz.) that has all of the above properties. PEO is also very tacky and many materials readily adhere to it, thereby making PEO an excellent rapid prototyping support material.
Furthermore, PEO is not as hygroscopic compared to other commercial water soluble polymers including polyvinyl alcohol and polyethylene oxide, and thus PEO possesses significantly greater dimensional stability in ambient humid atmosphere compared to these other polymers. Moreover, PEO can be extruded at higher temperatures without decomposing and having its melt viscosity change with time.
In another aspect of the present invention, PEO is used as a fugitive mold material for casting ceramic slurries, e.g. for ceramic green body fabrication, and also preparing polyurethane or epoxy parts by pouring reactive mixtures of these liquid precursor materials into a mold which is precision machined from bulk PEO stock. Thus, in accordance with the present invention, parts can be subsequently extracted from the mold by placing the entire part in a water bath after the slurry or precursors are cured so that the water dissolves the PEO and leaves the fabricated polymer or green ceramic part behind.
This unique polymer PEO, not heretofore suggested for use asan extrusion freeform fabrication material, greatly facilitates the extrusion free form fabrication of parts, as well as for casting ceramic slurries.
These and other objects, advantages and features of the present invention will be more fully understood and appreciated by reference to the detailed description which follows.